This invention relates to drive systems for domestic electrical appliances, and especially though not exclusively to such systems for kitchen appliances such as food processors.
Drive systems for kitchen appliances are required to fulfill many criteria, which critically influence various aspects of their design and construction and, in many cases, present the need for compromise. For example a single appliance, such as a food processor can be required to perform tasks which dictate the ability to operate with widely varying speed/torque characteristics, and such performance has to be achieved in a reliable and user-friendly manner, without the generation of undue amounts of noise and/or vibration, in a relatively inexpensive appliance of compact dimensions, of which the operating height is of particular concern.
Many drive systems have been adopted in efforts to optimise the overall performance/price/configuration package offered to the consumer, but most have fallen short of the ideal requirements, at least in some respects.
It is an object of this invention to provide a drive system for a domestic appliance, which system adopts an approach to the basic drive layout which enables at least one of the criteria mentioned above to be addressed from a novel perspective.
According to the invention from one aspect there is provided a drive system for a domestic appliance, the system providing inner and outer coaxial drive outlets operative at different speeds and comprising a first limb, incorporating an electric drive motor and a drive shaft driven by said motor and coupled to said inner drive outlet to drive it at a selected speed, and a second limb including a rotary component, the limbs being disposed and maintained in spatially fixed relationship to one another; a first speed reduction mechanism coupling the drive shaft to the rotary component of the second limb and a second speed reduction mechanism coupling the said rotary component to said outer drive outlet.
Preferably, said rotary component comprises a further shaft disposed substantially parallel to the drive shaft of said motor, whereby both of said first and second speed reduction mechanisms can be directly connected between said shafts, giving positive driving capability and permitting the construction to be dynamically balanced to reduce wear and to control noise and vibration, even when the system is operated under adverse conditions.
Both limbs of the system are preferably rigidly mounted to, and supported by, a common framework of support members to promote robust and smooth operation.
According to the invention from another aspect there is provided a drive system for a domestic appliance, the system comprising a first limb including an electric motor having a drive shaft provided with a coupling intended to provide a first drive outlet operative at a selected speed, and a second limb including a further shaft disposed substantially parallel to the drive shaft and offset therefrom, a first speed reduction mechanism coupling the motor to the further shaft and a second speed reduction mechanism coupling the further shaft to a second drive outlet concentric with the first drive outlet, and wherein rigid mounting means is provided to mount the two shafts in said substantially parallel relationship to one another.
The incorporation of the motor directly into one of the operative limbs advantageously imparts rigidity into the drive system as a whole.
The selected speed can, in accordance with either aspect of the invention, conveniently be the operational speed of the motor, and is typically in the range 10,000 to 20,000 rpm.
Preferably, in accordance with either aspect of the invention, the motor is a series motor of short axial length, measured along the drive shaft, which permits the height of the drive system, and therefore of the appliance as a whole, to be kept acceptably low, with the drive shafts disposed upright.
Preferably, in accordance with either aspect of the invention, the coaxial drives operate respectively at high speed, direct from the motor, for blending purposes, and at a lower speed suitable for food processing.
It is further preferable, as regards either aspect of the invention, that the speed reduction mechanisms comprise respective belt and pulley mechanisms disposed parallel to one another. This provides reliable and cost-effective speed reduction without unduly increasing the axial length, thus the operative height, of the overall system.
Where two belt and pulley mechanisms are employed they can, if desired, be configured to impart identical speed reductions, thus permitting duplicate components to be used; allowing economies of scale to be taken into account and increasing the cost effectiveness of the system.
More preferably still, as regards either aspect of the invention, the speed reduction mechanisms are respectively disposed to either side of the motor in an axial direction, (above and below the motor respectively in operation) thus providing a stable system with good sound and vibration performance.
The system may, in some embodiments, comprise first and second mounting plates, disposed parallel to one another and on opposing sides of (above and below respectively) said motor, in the axial direction. In these circumstances it is preferred that the first and second speed reduction mechanisms are disposed respectively below the second mounting plate and above the first mounting plate.